Port Checker
Enter a hostname and port number to test if the port is accessible from the internet.
Common ports:
Server-side TCP check — tests external port accessibility from our servers.
How to use Port Checker
The Port Checker tests whether a specific TCP port on a server is open and accepting connections from the public internet. Services listen on ports — web servers on 80 and 443, mail on 25 and 587, SSH on 22 — and a port that appears closed from outside is the classic symptom of a firewall rule, a service that is not running, or a router that is not forwarding traffic. Use this tool to confirm that a service you just deployed is actually reachable, or to verify that a port you expect to be blocked really is closed to the outside world.
- Enter the server hostname or IP address you want to test.
- Enter the port number, or pick a well-known service port.
- Click Check to attempt a TCP connection from our servers.
- Read whether the port is open (accepting connections) or closed/filtered.
- Adjust your firewall or service configuration and re-test as needed.
Open, closed and filtered ports
A port can be in one of three states. Open means a service accepted the connection. Closed means the host replied but nothing is listening on that port. Filtered means a firewall silently dropped the probe, so no reply came back at all and the attempt times out. The difference matters: a closed port suggests the service simply is not running, while a filtered port points to a firewall or security group actively blocking access. This tool reports which behaviour it observed so you can target the right fix.
Common ports and their services
Most everyday services use well-known port numbers, and memorising the common ones speeds up troubleshooting. Web traffic uses 80 and 443, SSH uses 22, and the various mail protocols spread across 25, 465, 587, 110, 143, 993 and 995. When a service is unreachable, the first check is whether its standard port is open from outside; if it is closed but the service is running locally, the problem is almost always a firewall or port-forwarding rule in between.
| Port | Service |
|---|---|
| 22 | SSH |
| 80 | HTTP |
| 443 | HTTPS |
| 25 / 587 | SMTP (mail) |
| 3306 | MySQL |
Glossary
- TCP port
- A numbered endpoint on a host that a network service listens on for connections.
- Open port
- A port where a service accepted an incoming connection.
- Filtered port
- A port where a firewall dropped the probe, producing no response.
- Firewall
- A system that allows or blocks network traffic according to rules.
- Port forwarding
- A router rule that directs external traffic on a port to a specific internal host.
Related reading
Frequently Asked Questions
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Why use Port Checker?
- Real-time DNS lookups using live resolver queries
- Supports IPv4 and IPv6 addresses
- No software to install — runs entirely in the browser
- Results include TTL values and record priority
Common use cases
- Verify DNS propagation after updating nameservers
- Check MX records when troubleshooting email delivery
- Look up SPF/DKIM/DMARC records for email security audits
- Test whether a SSL certificate is valid and up to date
- Find the IP address behind a domain name
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